This invention relates to a cam switch mechanism, and to control devices which incorporate this mechanism and which are thereby able to control a wide range of different types of apparatus and systems. The invention is particularly concerned with a pullkey, which is one such control device incorporating this cam switch mechanism.
Although the cam switch mechanism is described hereinafter in relation to a pullkey, it should be understood that the cam switch mechanism in its broadest aspects is not limited to this particular application. Nevertheless, the invention is particularly concerned with pullkeys, and with a pullkey which is simple to operate, has a direct on-line switching action, can be produced relatively easily and cheaply, is attractive in appearance, has a low profile for unobtrusive mounting, and is capable of use in a variety of different operational systems.
Pullkeys are designed for use in particular alongside conveyors and other mechanised equipment where safe protection and emergency stopping of the conveyor or other machinery is required. For example, pullkeys are used in conjunction with conveyors and other systems operating at coal faces, alongside roadways, and in various industrial applications. Pullkeys are usually mounted alongside or adjacent to the conveyor or other machinery at intervals, depending upon site requirements, with a single-ended type pullkey at each end of the line and with a number of double-ended pullkeys spaced in between. It is important for such pullkeys that they should have a positive, reliable switch action. The switch mechanism within the pullkey must be able to perform at least two functions. Firstly, in response to a pull on the interconnecting pullwire or pull-rods the switch mechanism must initiate lockout, i.e. produce a positive and effective stopping of the associated conveyor or other equipment. Secondly, the switch mechanism must be able to provide for signalling, i.e. to provide a remote indication that a particular pullkey has been actuated and to enable further pulls on the pullwire to signal or trigger an alarm. In operation, pulling of the pullwire will operate the switch mechanism which will both initiate the lockout action and also produce a signal indication. Pullkeys conventionally also incorporate a lockout knob. In latching type pullkeys the lockout knob is actuated automatically when the pullwire is pulled, and the lockout knob and the system can only be reset by a positive manual resetting operation at the pullkey itself. In non-latching type pullkeys the lockout knob is not actuated automatically and can only be actuated locally by a manual rotation of the knob at the pullkey itself. Electrical lockout initiated by a pull on the wire in the case of a non-latching pullkey is not linked to a rotation of the lockout knob which would give mechanical latching and prevent remote resetting of the system. The pull on the wire just switches a relay or contactor to stop the system, and resetting can be carried out at the central control unit, not at the pullkey.